1. Field of the Invention
This invention relates to a high-molecular blend, a functional porous material and a process for manufacturing the same, and a functional composite material and a process for manufacturing the same.
2. Description of the Related Art
There are known porous materials, such as polyurethane or other plastic foams, and sponge, which are manufactured by foaming the raw materials by a reaction forming cells, or by employing a foaming agent, or N.sub.2 or CO.sub.2, or by mechanical stirring. Although these materials can be manufactured by simple processes, the cells formed by foaming are considerably large, and it is difficult to form microscopic cells.
There are also known functional separation membranes which are manufactured by stretching (e.g. GORE-TEX.RTM.), by a physical method, by making holes by etching, by adding a soluble substance and dissolving it away, or by employing a nonwoven fabric. All of these materials have a fairly microscopic porous structure, but have the drawbacks of being low in uniformity and porosity.
It is well known that the morphology of a blend of different substances depends on the proportions in quantity of the blended substances, their compatibility, the blending conditions, etc. Referring, for example, to the proportions in quantity, it is often the case that both of two components I and II of a blend form continuous phases if their proportions in quantity are substantially equal, as shown in FIG. 3. If, on the other hand, one of the components I has a significantly greater proportion, it is very likely that the component I may form a continuous phase, while the minor component II is scattered in discontinuous phases, as shown in FIG. 4. This is particularly the case when the component I has a proportion of 70% or more, while the component II has a proportion of 30% or less. This tendency coincides well with the fact that balls filling a cube cannot occupy more than 74% of its volume.
As a matter of fact, there is literature containing the following statement ("`Polymer Alloys`--Fundamentals and Applications", Edited by The Society of High-Molecular Substances, and Published by Tokyo Kagaku Dojin, page 380):
"A component having a high volume percentage tends to form an ocean phase. A component having a volume percentage of 75% or more forms an ocean phase, while a component having a volume percentage of 25% or less forms an island phase, irrespective of any other conditions. The phase formed by a component having a volume percentage of 25 to 75% depends on the blending conditions."
The morphology of a blend, of course, depends largely on the compatibility of its components, too. The higher their compatibility, the more likely it is that the microscopic separation of phases may occur, and the more likely it is that even a component having a relatively small volume proportion may form a continuous phase. If, on the other hand, their compatibility is very low (as in a mixture of water and oil), their mixture shows a considerable microscopic phase separation if it is strongly stirred, but their phase separation is very unstable and changes to a macroscopic one with the passage of time.
Anyway, it is generally difficult to form a stable three-dimensional continuous phase from a minor component having a volume percentage of 25% or less in its blend with a major component having a volume percentage of 75% or more.
It is generally true that a minor component dispersed as discontinuous (island) phases in a major component can hardly exhibit its desirable properties, since they are hidden behind the properties of the major component. It is, therefore, most advisable to establish a system in which the minimum possible amount of a minor component is uniformly distributed to form a three-dimensionally continuous network skeleton structure, so that a major component may exhibit its desirable properties to the maximum possible extent, while the minor component makes up the undesirable properties, or drawbacks of the major component. In a mixed system containing 25% or less of a minor component and 75% or more of a major component, however, it is difficult to form a stable three-dimensionally continuous phase of the minor component, since the minor component generally tends to be scattered and form discontinuous phases, as hereinabove described. It is impossible to form a three-dimensionally continuous network skeleton structure of the minor component, except in very rare cases. Moreover, it has hitherto been difficult to obtain porous materials having microscopic cells and the conventionally available functional separation membranes have the drawbacks of being low in the uniformity of their porous structure, and in porosity, as hereinabove pointed out.
If it is possible to prepare a disperse system in which the minimum possible amount of a minor component forms discontinuous (island) phases in a major component and is uniformly distributed to form a three-dimensionally continuous network skeleton structure, the removal of the major component from the system makes it possible to obtain a functional porous material having a three-dimensionally continuous network skeleton structure formed by the minor component. It is, however, difficult to form a three-dimensionally continuous phase of a minor component, since it generally tends to form discontinuously scattered phases, as hereinabove stated. As a matter of fact, there has hitherto not been provided any mixed system containing a minor component forming a three-dimensionally continuous phase.